As can be seen by reference to the following U.S. Pat. Nos. 5,276,253; 4,942,929; 4,968,187; and 5,109,933; the prior art is replete with myriad and diverse methods and apparatus for backfilling boreholes, circular shafts, and the like.
While all of the aforementioned prior art constructions are more than adequate for the basic purpose and function for which they have been specifically designed, none of these prior art methods employ the simultaneous introduction of feedstock in conjunction with the application of compressive and shear stresses to the deposited feedstock resulting in a high quality seal that will satisfy rigorous EPA, NRC, and other agency regulations for compliance.
A major concern in sealing technology is the compliance of such seals to strict environmental regulations. Uncertainty in performance assessments of sealing components will be minimized by producing a higher quality seal at the outset. Current technology for emplacement of these materials depends on the application. For boreholes, grout or concrete is pumped to the desired seal location, bentonite or crushed rock and bentonite are pneumatically or hydraulically transported to the desired seal location, and crushed salt is essentially poured into the holes. For shaft applications, concrete is poured at the seal location. Bentonite and crushed salt would be emplaced in compressed blocks or tamped in place using standard hand-held civil construction cold-tamping equipment in shafts.
A deficiency in the current emplacement techniques for seals lies in the poor control of the in situ emplacement density for crushed salt and bentonite/rock seals and questions of chemical compatibility, longevity, and interface characteristics for grout and concrete seals.
Seals are typically used to reduce or control the flow of fluids from the region in which they are stored to the accessible environment. Crushed salt seals for example, are effective only after the crushed salt seal has achieved about 95% relative density to the intact rock.
Current technology for emplacing the crushed salt can only achieve about 80-85% relative density immediately upon emplacement. The crushed salt will, however, reconsolidate due to creep closure of the surrounding rock. This creep closure is expected to produce 95% relative density after about 100 years. Short-term components such as concrete and bentonite are used to provide temporary sealing for a limited time period while the salt seal matures. Certain scenarios suggest that the reconsolidation may be slowed or stopped if the crushed salt becomes saturated prior to complete reconsolidation.
Clearly then, a technique that allows emplacement of seals at relative densities above 85%, perhaps as high as 90-95%, would greatly reduce the uncertainty associated with the long-term sealing of hazardous or radioactive materials, or other storage scenarios.
As a consequence of the foregoing situation, there has existed a longstanding need for a new technology that will produce improved borehole seals having lower permeability, greater seal and interface strength, effective quality control, and enhanced chemical compatibility immediately upon emplacement; and, the provision of such a method and apparatus is a stated objective of the present invention.